Android 数据库

Android

功能

实现数据库基本的增删改查。

代码

MainActivity：

public class MainActivity extends Activity {
    private Button button1, button2, button3, button4;
    private static MySqlHelper mySqlHelper;
    private static SQLiteDatabase db;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mySqlHelper = new MySqlHelper(MainActivity.this, "student_inf.db",
                null, 1);
        db = mySqlHelper.getWritableDatabase();
        button1 = (Button) findViewById(R.id.button1);
        button2 = (Button) findViewById(R.id.button2);
        button3 = (Button) findViewById(R.id.button3);
        button4 = (Button) findViewById(R.id.button4);
        // 添加数据
        button1.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // 加入2个数据
                ContentValues values = new ContentValues();
                values.put("name", "stu01");
                values.put("password", "abc");
                db.insert("student", null, values);
                ContentValues values2 = new ContentValues();
                values2.put("name", "stu02");
                values2.put("password", "def");
                db.insert("student", null, values2);
                query();
            }
        });
        // 删除数据
        button2.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Cursor cursor = db.rawQuery(
                        "delete from student where name = '" + "stu01" + "'",
                        null);
                cursor.moveToNext();
                query();
            }
        });
        // 修改数据
        button3.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                ContentValues values = new ContentValues();
                values.put("name", "stu03");
                values.put("password", "hig");
                db.update("student", values, "name=?", new String[] { "stu01" });
                query();
            }
        });
        // 查询数据
        button4.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                query();
            }
        });
    }
    // 打印数据库中所有的name
    private static void query() {
        Cursor cursor = db.rawQuery("select * from student", null);
        System.out.println("打印数据库中所有的name");
        while (cursor.moveToNext()) {
            System.out.println(cursor.getString(1));
        }
        cursor.close();
    }
}

MySqlHelper：创建数据库表 student，其中包括 name和password两列。注意 execSQL 语句的格式，结尾是有个括号的！

public class MySqlHelper extends SQLiteOpenHelper {
    public MySqlHelper(Context context, String name, CursorFactory factory,
            int version) {
        super(context, name, factory, version);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        // 创建数据库表 student
        db.execSQL("create table student(_id integer primary key autoincrement,"
                + "name varchar(20)," + "password varchar(20))");
        System.out.println("onCreate 被调用");
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        System.out.println("onUpgrade 被调用" + oldVersion + "--" + newVersion);
    }
}